There are many applications where it is necessary to protect a-c load equipment from power surges and voltage transients which could deleteriously affect and possibly damage such equipment. This protection is particularly important for equipment comprising highly sensitive or complex multiple loads susceptible to electrical noise. For example, modern sophisticated data processing equipment includes highly sensitive electronic components which are particularly susceptible to damage or loss of stored data therein due to reactive voltage spikes occurring as a result of power surges in the feeder lines, switching transients, or as a consequence of external causes such as lightning or corona discharges or merely due to the internal circuitry itself. Some of these conditions can also occur with respect to, and thus damage, sophisticated telecommunication and telephone equipment installations.
Numerous types of protective networks have been designed in an attempt to protect such equipment from these power surges and transients; but most of these existing protective networks have not been entirely satisfactory for all conditions of service. Specifically, it would be desirable that such protective networks be adapted for convenient installation with existing equipment, prevent the deleterious effects of such surges and transients occurring at the source, or as a consequence of the circuit breaker switching, as well as being effective to prevent reactive spike build-up or other spikes or noise at the load side of the network. This is especially true in many modern buildings where there are numerous electronic components, especially PC's, connected to one subpanel. In fact, it is not uncommon to have several thousand PC's in a single office building. Thus, the inventor has found that one source of noise and spikes can be a computer itself. The large number of PC's, printers, etc in many modern office buildings can make the building load generated noise a major problem. Furthermore, it would be desirable to provide such surge and transient protection in synergistic combination with power filtering, as well as to adapt such protective networks for convenient installation with, and therefore protection of, multiple type loads, i.e. 3-phase and single-phase loads.
One protective network that has been effective is disclosed in U.S. Pat. No. 4,675,772, the disclosure of which is incorporated herein by reference. This network provides power surge and transient voltage protection for a-c load equipment, and is illustrated in FIG. 1. The network 10 illustrated in FIG. 1 includes an L-C filter portion 11 and a pair of voltage suppressors 12 and 13. The voltages suppressors 12 and 13 are connected across lines 14 and 15 supplying a-c power to input terminals 1 and 2 of a load 16. As shown, the filter network 10 includes an inductor 11a and a capacitor 11b and is located PG,4 between the suppressors 12 and 13.
While the network disclosed in the incorporated patent works extremely well, it does introduce some costs into an overall system. Thus, reducing the costs associated with the protector network disclosed in the incorporated patent would further improve that network.
Accordingly, there is a need for a protector network for a-c equipment which has a minimum cost, yet is still as effective as the network disclosed in U.S. Pat. No. 4,675,772, and which can be incorporated in a building.